Four-point contact chain



1936- I R. w. DULL ET AL 2,056,602

FOUR-POINT CONTACT CHAIN Filed A ril 21. 1930 4 Sheets-Sheet 2[720675252715 RQQWZORJ WflaZZ Oct. 6, 1936. R. w. DULL ET AL 2,056,602

FOUR-POINT CONTACT CHAIN Filed April 21, 1930 4 Sheets-Sheet s1265977207202 WflzoZZ Oct. 6, 1936.

R. w. DULL ET AL FOUR-POINT CONTACT CHAIN Filed A ril 21, 1930 4Sheets-Sheet 4 fn'ven 250 715 072% 71722022 Patented Oct. 6, 1936FOUR-POINT CONTACT CHAIN Raymond W. Dull, Chicago, Ill., and EricGeertz,

Indianapolis, Ind., assignors to Link-Belt Company, Chicago, 111., acorporation of Illinois Application April 21, 1930, Serial No. 447,997

13 Claims.

Our invention relates to improvements in silent chain and has for oneobject to provide a new and improved form of silent chain whereinsilence and accuracy may be combined with v maximum length of liferesulting from increased areas of contact between chain and sprockets.Our invention in general may be described as a four working surfacechain, that is to say. a chain having two teeth on each link, each toothhaving two working surfaces, the working surfaces or working faces atthe opposed ends of the link being outside working faces, the surfaceson the opposed sides of each link tooth bounding the two sides of thepocket formed between the two teeth being interior working faces. Theseworking faces under various conditions and at various times all work bycoming into driving relation with opposed faces on the sprocket'teeth.Under some circumstances we may have four point contact in which allfour of the working faces on the link simultaneously engage workingfaces: on the sprocket. Under other circumstances we may have two pointcontact when only the two outside working faces engage sprocket teeth.Under some other circumstances we may have two point contact where theinterior working face on one tooth and the exterior working face onanother tooth of the link engage the sprocket. But we never have asituation where only two interior working faces of a single link engagethe sprocket simultaneously and we never have a situation where theinterior and exterior working faces of only a single chain tooth engagethe sprocket simultaneously. A further situation which is sometimesencountered is one when there is but a single point contact between eachlink and the sprocket and this single contact is always with an interiorworking face.

All of these possibilities are present when a single link'separate froma chain is placed upon the sprocket and especially the four workingsurfaces contact is only possible when a single link is placed upon asprocket and when such link is placed upon a sprocket having a longtooth with a root circle of excessively small diameter., When 'a singleone of our links is placed on a sprocket having a stub tooth, that is asprocket having a relatively short tooth with 0 a relatively largediameter root circle, inward movement of the link is prevented byengagement of the points of the link teeth with the root circle andunder these circumstances two point contact only is possible and thattwo 55; point contact always'is with one interior and one exteriorworking face of the chain link engaging cooperating sprocket toothworking faces.

As the individual link is moved outwardly along the sprocket tooth toand slightly beyond the pitch circle, this two point contact persists. 5But as the link is moved radially further away from the pitch circle, apoint is reached when only one point contact occurs.

The inter-relation of the articulating links normally prevents inwardmovementof the inl0 dividual links making up the chain inside the pitchcircle and there is a range of operation through which the chain mayelongate either by wear-or by stretch without interfering with this twopoint contact but as the length of the chain exceeds a predeterminedmaximum which varies for individual chain and sprocket combinations thepoint is reached where as the chain travels around the sprocket only onepoint contact occurs. This is because of the angularity of the sprocketteeth, the sprocket tooth engaging the outside working face losingcontact so that as the chain is stretched or increases in length beyonda certain point we have only one point interior contact.

This particular relation between the links, be they separate or in achain, and the sprocket results from the fact that the working faces ofeach individual link are generated and they are generated with initialclearance as will hereinafter appear. This generation is so related thatthe clearance is taken into consideration and results from the initialclearance generation so that there is no possibility of locking orbinding of individual chain links on the sprocket teeth.

Our invention is illustrated more or less diagrammatically in theaccompanying drawings, wherein Figure 1 shows the generation of a fourworking surface link with clearance showing the generation for both linkteeth on the same figure;

Figure 2 shows the working surfaces resulting from generation about theright hand axis of generation in Figure 1;

Figure 3 shows the working surfaces resulting from generation about theleft hand axis of generation in Figure 1;

Figure 4 shows for purpose of comparison, the generation of an imaginarytype of four point contact link without clearance wherein the generationis about a single and not about two spaced axes of generation;

Figure 5 shows a single link in position on a long tooth sprocket withlink inside the pitchcircle showing four point contact;

Figure 6 shows a single link on the sprocket in the position it wouldoccupy on the pitch circle showing two point contact;

Figure 7 shows a single link on the sprocket in the position it wouldoccupy outside of the pitch circle showing two point contact;

Figure 8 shows a link farther beyond the pitch circle and showing onepoint interior contact;

Figure 9 shows a single link on a stub tooth sprocket showing how theincreased diameter of the root circle of the sprocket prevents anythingexcept two point contact;

Figure 10 shows the action of our chain as it winds under tension ontoand off of a sprocket.

Figures 11 and 12 are diagrammatic views illustrating a method ofdetermining the generated tooth form or profile.

Like parts are indicated by like characters throughout the specificationand drawings.

A is a sprocket having in the preferred form sprocket teeth A whichteeth are short so that the sprocket may be described as a stub toothsprocket. In the modified form shown in Figure 5, for the purpose ofillustration only, the sprocket tooth B has a long tooth 13 instead ofthe stub tooth A as shown in the other drawings. A is a chain made up ofa series of separate chain links A, each link being perforated at A A sothat pintle pins A may join a series of links together to form a silentchain belt. A and A are link teeth adapted to interlock with thesprocket teeth and the teeth are so related and the belt is so built upthat it makes no difference which direction the chain goes and makes nodifference whether the chain drives the sprocket or the sprocket drivesthe chain, the relation between chain teeth and the sprocket teethremaining the same for all conditions so that the chain may wind onto oroff of the sprocket without interference. Our chain is primarilyintended for operation in connection with a stub tooth sprocket whereinthe relation between the root diameter and the pitch diameter is suchthat a chain wound about the sprocket is limited in its inward movementtoward the center of rotation by engagement between the ends of thechain teeth and the root circle as indicated in Figure 9 so that thereis never actually any thing other than two point contact as shown inFigures 6 and 10 or one point contact as shown in Figure 8 and fourpoint contact thus becomes altogether impossible. If a longer tooth wereused, then it might be possible to push the chain or the chain linksdown into the position shown in Figure 5 when four point contact wouldresult but this means the use of a weaker sprocket and one moreexpensive to manufacture. While under some circumstances such a sprocketmight be used, it is ordinarily undesirable and even though such asprocket is used the chain when at work lies in position with its linksas shown in Figure 6 or 10.

Referring now to Figure 1, it will be noted that the distance 0-0;,which is the minimum distance from the pintle axis to the interiorworking surface equals the distance 0-1) which is the minimum distancefrom the pintle axis to the exterior working surface and this relationprevails on both ends of the link. This relationship, together with thefact that the sprocket teeth are symmetrical means that there willalways be, as long as the chain is on the pitch circle, two pointcontact between the leading faces of the chain teeth and their adjacentsprocket teeth when the chain is driving and the following faces of thechain teeth and their adjacent sprocket teeth when the sprocket isdriving. When the chain is old or stretched and lies sufficientlyoutside the pitch circle then there is only contact with one or theother of the interior faces of the link either the leading or thefollowing as the case may be.

Now referring to Figure 10, if we assume that the gear is driving, thesprocket tooth 9: drives the chain by interior contact with the chaintooth x engaging its following side. The sprocket tooth 22 engages thefollowing faces of the next chain tooth, having inside contact withlinks X and outside contact with links X. The same is true part Wayaround the gear to some point perhaps at m where there is no contact atall after which the contact relation is reversed and the chain begins topull on the sprocket. A reversal of contact surfaces here takes place.

In the manufacture of silent chain and silent chain sprockets,experience shows that the obtaining of the proper clearance between thechain teeth and the sprocket teeth is of the utmost importance. Perhapsquite as important is the obtaining or generating of correctly relatedsprocket and chain tooth surfaces, and our present invention to a veryconsiderable extent depends upon the method in which the clearances areobtained.

If we select the sprocket tooth contour and then use this tooth shape ona cutter to generate the chain, we will generate all four working facesof the chain link, as in Figure 4, that is, the two working faces ofeach link tooth but there will be no clearance between the chain and thesprocket and such a chain will not be satisfactory in operation. Inorder that the generation may be correct, the clearance may be correct,and chain operation will be correct, we generate pairs of chain toothfaces separately by displacing the center line of the link first to oneside and then to the other side of the center line of the straddledsprocket tooth. In other words, instead of generating the link surfaceswith the link center line coinciding with the radial center line of thestraddled generating sprocket tooth, we displace the link center line toone side or the other side of said tooth center line, thus producing thedesired clearances. For the sake of brevity and clarity the radialcenter line of the straddled generating sprocket tooth will hereinbelowbe referred to as the straddled tooth center line.

In Figure l C is the center line of the straddled generating sprockettooth and R and L represent the displaced link center lines. Whengenerating the required contours of the link teeth from thepredetermined sprocket tooth form, the center line of the link isconsidered to coincide first with R and then with L to obtainrespectively the link tooth faces shown in Figures 2 and 3. It will benoted that generation about one of the displaced link center lines givesthe required outline for the interior face of one link tooth and theexterior face of the other link tooth. The other pair of link toothsurfaces are similarly obtained by generation about the link center lineoppositely displaced from the straddled tooth center line. It will befurther noted that the center line of the link during the generatingprocess lies between the straddled tooth center line C and the exteriorlink tooth face obtained by the generation.

In this connection reference is made to oopending application of WilliamF. Brandt, Serial No. 351,199, filed March 1929, for Silent chain,wherein there is a detailed discussion of the terms used in connectionwith silent chain and it will be understood that our invention relatesto the same general kind of generation and is a chain having the samekind of conjugate relation between the working parts, the differencebeing that where Brandt merely discloses the idea of chain generation wehave gone a step farther and by generating the working faces aboutdisplaced lines of generation we are enabled to get a different kind ofchain relation between the chain and the sprocket.

The use and operation of our invention are as follows:

For the purpose of analyzing and explaining the characteristics of thechain made according to our process we will first consider a singlechain link placed in contact with a sprocket.

Each link has two teeth and each tooth has two working surfaces, two ofthese surfaces being inside working surfaces forming the two sides ofthe pocket between the two link teeth, the two other surfaces beingoutside working surfaces, one at each end of the link. If the diameterof the root circle of the sprocket is small so that the sprocket is along tooth sprocket, then a single link may be placed on the sprocket insuch a way that all four of the working surfaces engage working surfaceson the sprocket teeth. Under these circumstances and with a sprocketdesigned for this chain the centers of articulation or the pivot centersof the link will fall inside the pitch circle.

If, however, as in our preferred form, the root circle is a maximum, wehave what is called a stub-tooth sprocket, then the points on the twochain teeth, which points take the form preferably of rather sharplycurved surfaces between the working faces, engage the root circle of thesprocket and by such engagement the inward radial movement of the linkis limited, so that only two point contact is possible. This contacttakes the form of simultaneous inside and outside contacts between asprocket tooth and one inside working face on the link, and one outsideworking face on the link, this two point contact being related toworking faces pointing in the same direction.

If the link is moved angularly with respect to the center of thesprocket, we get two point contact with the other two working faces.This situation may prevail even though the link lies with its centers ofarticulation inside the normal pitch circle.

If, now, the link is placed on the sprocket at a point at or evenoutside of the pitch circle, we still can get this two point contact,but as the link is moved radially farther and farther away from thecenter of rotation and so out considerably beyond the pitch circle, wereach a point where, owing to the angularity of the sprocket teeth, onlyone point contact is possible and this one point contact is interiorcontact.

These peculiar relations between sprocket teeth and chain teeth arepossible because the chain teeth are generated with initial clearance.Such generation with initial clearance gives a silent chain with thebest possible relation between the chain and the sprocket asdistinguished from earlier methods where the chain tooth contour isgenerated by the sprocket and then the space between the teeth isarbitrarily increased to provide clearance. This results be" cause eventhough we generate the chain teeth properly, when we separate themarbitrarily we change the relation between them and the sprocket teethand they are no longer in true generated relation with respect to thesprocket teeth.

This generation, with initially generated clearance, is obtained bygenerating the interior working face of one tooth and the exteriorworking face of the other tooth about the displaced link center line.Both pairs of working faces are similarly generated, the clearancebetween them being determined by the distance between these displacedcenter lines R and L shown in Figure 1.

When a plurality of links, such as those above discussed, are assembledto form a silent chain, it will be understood that the relation betweeneach individual link in the chain and the sprocket will ordinarily bemodified by the fact that such link is assembled into a chain andarticulated with other links, and especially since such a chain isintended to be used with a stub tooth sprocket the four point contactreferred to above as a theoretical possibility will never occur inactual practice.

The two point contact will always occur with the chain links on orslightly outside of the pitch circle.

As the chain elongates under load and wear, the pitch length increasesuntil a point is reached when each link rides out so far on the sprocketthat single point contact only occurs, and this contact is always insidecontact between one face of the sprocket tooth and one inside workingface of the link.

Under some circumstances when the single link above referred to isplaced on a sprocket having teeth of slightly different shape from thosewith which it is primarily intended to cooperate it may happen thatinstead of getting four point contact with the link inside the pitchcircle we only have two point contact with only the two outside workingfaces of the link touching the sprocket, but we do not want, do notintend to get and on a satisfactorily operating sprocket never do get acondition where we have two point interior contact. In other Words witha long tooth referring to a single link we always F get either fourpoint contact or two point exterior contact but never two point interiorcontact and none of these situations ever occur under working conditionswhen the links are assembled to form a silent chain belt and are in rdriving relation with the sprocket.

We thus have a chain sprocket combination where with the chain as closeto the center of rotation of the sprocket as possible two point contactoccurs and this two point contact continues to occur as the chainstretches and so rides further out on the teeth until at some point inthe stretching of the chain or the wear of the chain the two pointcontact disappears and we have one point interior contact. Furtherstretching or wear of the chain will continue until the chain has becometoo long to work satisfactorily on the sprocket but up to the time whenthe chain is no longer satisfactory we still get only single pointinterior contact.

In a drafting room method for determining the form of are generatedbetween the pin centers of a link by a given sprocket tooth form, theremay be an arbitrary selection of 1. The pitch of the chain; 2. Thediameter of the pitch circle of the chain on the sprockets; 3. The toothform of the sprocket wheel; 4. The outside diameter of the sprocket.

As a basis for the generating process, the following conditions desiredin the resulting chain are assumed:

1. Constant angular velocity in the sprocket combined with constantlinear velocity in the chain entering the sprocket, the velocity of thechain being equal to the linear velocity of a point on a sprocket tooth(extended if necessary) which lies on the pitch circle.

2. The points of articulation or pin centers of the assembled chainshall enter the sprocket on a line tangent to the pitch circle of thechain on the generating sprocket.

One method of procedure to obtain the desired tooth profile may be asfollows:

Select arbitrarily a sprocket of any convenient size or given pitch andnumber of teeth with a definite form of teeth as shown at S in Figure11. Draw an arc of the pitch circle of the sprocket as A-l4, Bl4, A|5,T-l of any convenient length. Draw the straight line T, B-I3, B--|2,A|3, A--l2 tangent to the arc of the pitch circle of the sprocket torepresent the pitch line of the chain as it approaches the sprocket.Also draw the straight line T-l, Bl5, A-l'!, B-l'l tangent to the arc ofthe pitch circle of the sprocket to represent the pitch line of thechain during recession from the sprocket.

On thin transparent celluloid or tracing paper mark two points spacedapart a distance equal to the pitch of the assembled chain. Call thesepoints of articulation A-l 2 and B-| 2. Place the points AI2 and B-l2 ofthe transparent sheet on the pitch line of approach Al2, A|3, B-|2, Bl3,in some relative position tothe first engaging tooth of the sprocket asS. Displace this tracing to the right or left as the case may be, adistance equal to the distance between the center line C and thedisplaced link center lines R, and L and in all subsequent positioningof this tracing use whichever position we have started with so that oneinside and one outside face of the link will be generated by the lefthand displaced center line and the opposed inside and outside faces ofthe link will be generated by the right hand side if the work is done asbelow pointed out.

The relation of the points Al2 and Bl2 to the profile S of the tooth maybe taken arbitrarily and conjugate profiles made for the relationassumed, but a preferred location of A-l2 and B-| 2 relative to profileS is such as to make the tooth profiles symmetrical to A-l2 and B-IZ asshown. Having located the link and tooth relation for the first toothengaged, the profile S of the tooth is traced on the transparent sheet.

The next step in the procedure is to move the transparent sheet a smalldistance toward the sprocket with points A-I2 and Bl2 always lying onthe pitch line and consider that the sprocket turns through an anglesuch that the linear displacement of the chain corresponding to theangular displacement of the sprocket gives uniform motions for both.This position mentioned is shown as Sl for the tooth profile AI3 and Bl3for the position of the articulation points of the link. The profile S-lis then traced on the transparent sheet as before.

As the link approaches the point of tangency T, Figure 11, the pointB-l2 of the link follows the pitch circle of the sprocket as at Bl4 andthe profile of the link is modified accordingly.

The link profile for the side of recession of the link is drawn in asimilar'manner. The points A-I2 and B-l2 follow the pitch circle of thesprocket in the same direction as during the approach to the point of,tangency of the pitch line of recession, then follow the pitch line ofrecession. The development of the profile of recess is from the root ofthe link tooth to the point, which is the reverse procedure of thedevelopment of the approach profile.

Now draw on the transparent sheet a line tangent to all the tracings ofthe given tooth for the entering action and a second line tangent to allthe tracings of the given tooth for the recession action. Figure 12shows the complete double profile of the engaging parts of the link.These curve are the required outlines for the contact surfaces of thelink to be designed and will be in correct relation on the transparentsheet to the pin centers marked thereon. The remainder of the linkoutline may be drawn as desired with due regard to clearances and tostrength factors and may take, for example, the form illustrated inFigures 5 and 6.

We claim: 7

1. A link for silent chains and the like having sprocket engaging teeth,the working faces of each link tooth being generated about link centerlines located respectively on opposed sides of the straddled toothcenter line.

2. A link for silent chains and the like having sprocket engaging teeth,the working faces of each link tooth being generated about link centerlines located respectively on opposed sides of the straddled toothcenter line, the link center line about which the interior face of thetooth is generated being on the opposite side of the straddled toothcenter line from such face.

3. A link for silent chains and the like having sprocket engaging teeth,the working faces of the teeth which face in the same direction beinggenerated about one link center line and the working faces of the teethwhich face in the opposite direction being generated about another linkcenter line.

4. A link for silent chains and the like having sprocket engaging teeth,the working faces of the teeth which face in the same direction beinggenerated about one link center line and the working faces of the teethwhich face in the opposite direction being generated about another linkcenter line, the link center lines being respectively located onopposite sides of the straddled tooth center line.

5. A link for silent chains and the like having sprocket engaging teeth,the working faces of the teeth which face in the same direction beinggenerated about one link center line and the working faces of the teethwhich face in the opposite direction being generated about another linkcenter line, the link center lines being respectively located onopposite sides of the straddled tooth center line, the link center lineabout which each pair of faces is generated being located between thestraddled tooth center line and the exterior working face of the pair.

6. A link for silent chains and the like having two sprocket engagingteeth the Working faces of which are generated about link center linesoffset from the straddled tooth center line.

'7. A link for silent chains and the like having two sprocket engagingteeth, the working faces of which are generated about link center linesoffset from the straddled tooth center line, one interior and oneexterior working face being generated about each of such ofiset linkcenter lines.

8. A link for silent chains and the like having two sprocket engagingteeth, the working faces of which are generated about link center linesoffset from the straddled tooth center line, such center lines ofgeneration being located one on each side of the straddled tooth centerline.

9. In combination, a sprocket and a silent chain comprising a pluralityof articulating toothed links each of which in the chain is adapted tocome into intimate physical working contact with the sprocket with whichit is related, the relative size, shape and proportions of the engagingchain and sprocket links being such that when the chain is adjacent thepitch circle there is' a contact between one working face only of eachchain tooth and a co-operating working face of a sprocket tooth.

10. In combination, a sprocket and a silent chain comp-risingapluralityof articulating toothed links each of which in the chain is adapted tocome into intimate physical working contact with the sprocket with whichit is related, the relative size, shape and proportions of the engagingchain and sprocket links being such that when the chain is adjacent thepitch circle there is a contact between one working face only of eachchain tooth and a co-operating working face of a sprocket tooth andwherein as the chain moves radially outwardly from the pitch circle, aposition is reached where there is working contact between one toothface on each link only and a sprocket tooth.

11. In a silent chain drive, a sprocket and a silent chain passing aboutsaid sprocket, said chain including a plurality of articulating toothedlinks each of which in the chain is adapted to come into intimatephysical working contact with the sprocket with which it is related,there being means for maintaining contact between one working face onlyof each chain tooth and a cooperating working face of a sprocket tooth,during normal operation of the drive.

12. In a silent chain drive, a sprocket and a silent chain passing aboutsaid sprocket, said chain comprising a plurality of toothed links eachof which in the chain is adapted to come into intimate physical workingcontact with the sprocket with which it is related, having faces adaptedto be opposed to faces upon the teeth of said sprocket, each said linkbeing normally in contact with two teeth of the sprocket when the linkrests loosely upon the sprocket, one face only of each link toothengaging a sprocket tooth, there being means for maintaining contactbetween one working face only of each link tooth and a cooperatingworking face of a sprocket tooth, when the link moves radially outwardlytoward the pitch circle.

13. In a silent chain drive, a sprocket and a silent chain passing aboutsaid sprocket, said chain comprising a plurality of toothed links havingfaces adapted to be opposed to faces upon the teeth of said sprocket,each said link being normally in contact with. two teeth of the sprocketwhen the link rests loosely upon the sprocket, one face only of eachlink tooth engaging a sprocket tooth, there being means for maintainingcontact between one working face only of each link tooth and acooperating working face of a sprocket tooth, when the link movesradially outwardly toward the pitch circle and for making contactbetween one working face only on each link and a cooperative workingface of a sprocket tooth when the link is located appreciably outside ofthe pitch circle.

RAYMOND W. DULL. ERIC GEERTZ.

